1. Field of the Invention
The present invention relates to an image pickup apparatus, a control method therefor, and a computer-readable storage medium storing a control program for implementing the method, and in particular, to exposure control during motion with high shutter speed.
2. Description of the Related Art
Conventionally, at the time of shooting a subject using an image pickup apparatus, luminance level is adjusted so as to control the brightness of the subject to a substantially constant value. In general, an image pickup apparatus adjusts luminance level by controlling exposure time using a diaphragm mechanism or an electronic shutter which adjust the amount of light from a taking lens.
Further, when a subject is dark, the gain of an electric signal, which is an output from an image pickup device, is controlled using an image pickup apparatus itself, an external amplifier, or the like to broaden the range in which the subject can be controlled to an appropriate luminance level.
In a case where exposure time is controlled using an electronic shutter, exposure time needs to be short when a subject is bright. In general, however, because exposure time controlled using an electronic shutter is an integral multiple of a horizontal synchronous signal period of an image pickup device, the closer the exposure time to the horizontal synchronous signal period, the greater the degree to which luminance changes with a one-step change in exposure time.
According to, for example, Japanese Patent Publication No. 3861711 or Japanese Laid-Open Patent Publication (Kokai) No. H09-55878, in order to suppress changes in luminance, a luminance level of a subject is adjusted by adjusting an amplification unit while minimizing shutter speed within such a range as not to exceed the luminance level of the subject.
However, according to Japanese Patent Publication No. 3861711 or Japanese Laid-Open Patent Publication (Kokai) No. H09-55878, a gain is always added according to a luminance of a subject, resulting in noise in an image itself.